1. Field of the Invention
The present invention relates to an automatic transmission electronic control device which is attached within a casing of an automatic transmission.
2. Description of the Related Art
A conventionally known automatic transmission electronic control device of the aforementioned type has a substrate which is attached within a casing of an automatic transmission and which includes an electronic circuit for operating the automatic transmission (see Japanese Patent Application Laid-Open Publication No. 2002-12097 (pp. 3-6, and FIGS. 1-8)). The vehicular electronic control device described in this publication has an insulating sheet 24 and, mounted on its upper surface, a control unit 33 that controls the automatic transmission. A protective cover 34 covers the control unit 33 and is supported by bracket 11 which is attached to a control valve 3 contained within an oil pan 2. The bracket 11 is formed by press-working a metal plate or the like. The protective cover 34 is formed of plastic or metal and has a generally box shape opening downward. Thus, the control unit 33 is surrounded by the bracket 11 and the protective cover 34, so as to be protected from the lubricating oil in the automatic transmission. Therefore, short circuit of the control unit 33 due to metal particles formed by wear and the like and present in the lubricating oil is prevented. In some cases, however, immediately after a stop in operation of the automatic transmission, lubricating oil at a temperature raised during operation flows from high-temperature operating mechanisms, such as the torque converter, the oil pump, etc., into the oil pan 2, and therefore rapidly raises the temperature of the electronic control device, resulting in a thermal overshoot. In such a case, the heat is conducted via the bracket 11 having high heat conductivity into the space between the bracket 11 and the protective cover 34 that contains the control unit 33, thus rapidly raising the internal temperature within that space and therefore the temperature of the control unit.
Thus, although the insulating sheet 24 is interposed between the control unit 33 and the bracket 11, the heat of the transmission oil is conducted to the control unit 33, so that the temperature of the control unit 33 may exceed its service condition temperature range, and therefore the electronic control device may fail to operate normally. During operation, the temperature control unit 33 may sometimes become that of the electronic control device. If this situation continues, the temperature of the control unit 33 may exceed its service temperature range, and therefore the electronic control device may fail to operate normally.